Electron discharge device and method of manufacture



Nov. 29, 1932. H. L. CROWLEY ET AL ELECTRON DISCHARGE DEVICE AND METHOD OF MANUFACTURE Filed April 6, 1929 0 5 6 ma 1 5 Mil 1 WW "a0 07 44 n 1 Z Y mm. km

Patented Nov. 29, 1932 mass? UNITED STATES PATENT OFFICE HENRY L. CROWLEY, OF EAST ORANGE AND ROBERT M. CROWLEY, 0F JERSEY CITY, NEW JERSEY, ASSIGNORS TO HENRY L. CROWLEY & CO. INC., 0}? EAST ORANGE, NEW JERSEY, A CORPORATION OF NEW JERSEY ELECTRON DISCHARGE DEVICE AND METHOD OF MANUFACTURE Application filed April 6, 1929. Serial No. 352,967.

This invention relates to improvements in vacuum tubes, and also to methods of manu facturing and assembling electron discharge devices.

A principal object of the invention is to provide a thermionic space discharge device of the alternating current type which is capable of being used in radio circuits with a minimum of interference due to the alternating current supply.

Another object of the invention is to pro vide an electron emitter of the indirect heater type, which requires a minimum time interval between the application of heating current and the emission of electrons sufficient to pass a signal.

A feature of the invention resides in a cathode of the indirectly heated type suitable for use in electron discharge tubes together with a special form of insulating and spacing member for the cathode heater element.

Anoth r feature pertains to a hollow metal cathode which has within it a heater element, the ends of said tube being substantially closed by special insulating closures, serving also to hold the heater element in proper spaced relation within the cathode.

A further feature resides in the method of manufacturing the novel heater insulating and spacing members, according to the invention, whereby uniformity of results are ob tained.

Finally the invention provides the combination and organization of elements which go to make up an eilicient electron discharge device which is capable of volume production with uniformity of result, and in which the manufacture and assembly cost is very much reduced.

Other features and advantages will be apparent upon a consideration of the following detail description and the appended claims.

Referring to the drawing;

Fig. 1 shows an indirectly heated cathode member according to the invention.

Fig. 2 i a longitudinal sectional view of the device shown in Fig. 1.

Fig. 3 is a plan view of a closure and spacer element of Fig. 1.

Fig. 4 is a modification of the cathode element shown in Fig. 1 employing a coiled filament.

Fig. 5 is another modification of Fig. 1 in which the filament is straight and looped back upon itself. This figure also shows a. modified form of closure element according to the invention.

Fig. 6 is a still further embodiment of a closure member suitable for use with a looped filament.

Fig. 7 shows a still further modification of a cathode closure member.

Fig. 8 illustrates a preferred method of manufacturing the filament spacer and retaining members according to the invention.

Fig. 9 is a schematic view of a three-electrode tube embodying 'eatures of the invention.

Referring more particularly to Figs. 1 and 2 there is shown an electron emitting cathode of the indirect heater type comprising a relatively thin walled tube 1, which is preferably of a suitable metal such as iron, nickel, molybdenum, tungsten, or the like. Tube 1 is also preferably seamless in character in order that all points on the surface thereof may have as nearly as possible equal heat conducting and radiating characteristics. The internal diameter of tube 1 and the length thereof are designed in accordance with the conditions of service under which the tube is to be used. However, it is preferable to make the internal diameter as small as is consistent with manufacturing methods, and also with the size of filament to be used. The exterior surface of tube 1 throughout a portion of its length is coated in any manner Well known to the art, with a suitable electron emitting substance 2. The opposite ends of tube 1 are closed by means of insulating and spacing members 3 and 4 respectively. These closure members may consist of any suitable insulating material, however, it has been found that an insulating material of the character disclosed in copending application Serial No. 332,555 filed January 14, 1929, is extremely well suited for this purpose, as will be pointed out hereinafter.

Referring more particularly to Figs. 2 and ing parts f this emitter 3, the main body portion of each spacer member 3, t is preferably cylindrical in shape, being provided with a central longitudinal bore 5 and with laterally extending wing lugs G and 7 It will be noted that the body portion of the member 3, for example is oil slightly smaller external diameter than the internal diameter of tube, except for the portion provided with the wing lugs 6 The advantage of this particular shape of closure member will be described hereinafter.

In the embodiment shown in Fig. 1. the members 3, i are inserted within the opposite ends of the tube 1, and preferably it closely therein, so that accidental jars or normal heat expansions of the tube 1 will not cause any movement between the said members and the said tube.

The main cylinor'cal body portion of each member 3, a is preferably proportioned in accordance with the length of the tube 1 and the character of the filament 8, so that id filament vhcn passed through the bores 5 is accurately and centrally positioned within the tube 1 and is prevented from lateral displacement therein. If desired, the bores 5 may be just suiiicient-iy small to permit the filament 8 to pass therethrough, so as trictionally to grip the filament against lateral and longitudinal movement. In addition.

however, well known filament tensioning means (not shown) may be employed to take up any ezicessive longitudinal expansions or contractions of the filament, and to retain the filament in its assembled position.

From the foregoing description will be seen that there is provided an internally heated cathode 2 in which the heater element 8 is accurately positioned within the center of the cathode tube 1. Consequently when said filament is heated by the passage of current therethrough, the heat therefrom is radiated uniformly over the internal surface of the tube 1, and the cathode 2 is thus enabled to produce uniform emission. This uniformity of heat radiation is maint ined during" the operation of the tube, because of the accurate lit which can be ob .ined between the members 3, 4 and the tube 1, to permanently space the filament from the walls of the tube. Furthermore substantially the entire heat from the filamentis effective on the cathode 2, because of the heat confining character of the members 3, 4.

Referring to Fig. i there is shown another embodiment of the invention, where n the heater filament instead of being straight. is in the form of a coiled wire 10. The remainare JubstantialIy the same as shown. in connection with 2 and 3, and are designated by the s me numerals.

It has bly of the coiled filament within tube 1, that the straight end portions must be manipulatbeen found that during the assem-' ed by the operator so that when passed through the members 3, a the coiled portion is concentric within the tube. By means of the reduced body portion 01" members 3, 4; the operator is enabled to look down into the tube 1, around the side of the said members, while the latter are being placed in position. It the interior end of members 3, a were of greater diameter than tube 1, the operator would be obliged to rely solely on the concentricity ot' the bore for the accurate assembly of the filament. It is obvious that this assembly advantage may be further enhanced by notching or corrugating' the cylindrical body portion of members 3, l, so that, even when said members are in position, the operator may still view the position of the tilement and make the proper adjustments for concentricity, etc. Similarly the body portion of the closure members may be cut away in spider-shape manner, to facilitate this viewing during the assembly. This reduced diameter of the insulator closures with respect to tube 1 also possesses the desirable ad vantage that the assembly of the cathode as a whole within a vacuum tube is facilitated because of the greater clearance provided. If desired the side walls of tube 1 may be slotted to receive the wing portions of the insulator members 3, l.

5 shows another embodiment of the invention using a looped filament heater 11. In this embodiment, in order that the parallel loops of the filament may be accurately positioned and spaced within the tube 1, the members 12 and 13 are similar to the members 3, 4 of Fig. 1 except that two parallel bores spaced longitudinal bores is provided with a single bore 15 of the general shape shown in Fig. 6. This partielar form of closure is advantageous in that it avoids threading of the looped end of the filament wires 11 through the small bores. For example, the member 1 1 may be used in place of the upper member 12 of Fig. 5, in which case the lower member 13 hereinabove described serves for the purpose of spacing the filament wires 11 apart from each other, while the bore 15 in the member 14- serves to retain the filament as a whole against lateral movement .vith respect to the tube 1. With this combination it is obvious that the filament 11, after being threaded through the member 13 may be re tained in proper position by simply posi tioning the member 14 within the upper end of tube 1, so that the looped end of the filament passes through the bore 15.

7 shows anothe' embodiment of the vnn 1.1.-

invention in which the portion 16 of the filament spacer and closure member is of larger diameter than the portion 19, which latter part fits within the cathode tube. This particular embodiment, however, while it possesses the advantages of closing the end of the cathode tube, and rigidly spacing the filament as already described, requires a great deal more material than the embodiments shown in Figs. 1 to 6 inclusive, since in these latter embodiments the only portions that are larger than the diameter of the cathode tube are the wings 6 and 7, which however, may be made very small and thin, as required. Furthermore the embodiments of Figs. 1 to 6 enable the cathode conducting strip 9 to be carried straight up over the members 3, this serving as an additional insurance against displacement of the members. Furthermore, the design of Fig. 7 cannot be made in contin uous lengths because of the diiierence in diameter of the portions 18 and 1f). \Vith the en'ibodiments shown in Figs. 1 to 6, on the other hand, the members may be made in any desired lengths by an extrusion process. For example as shown in Fig. 8, a length of insulating material may be formed by extrusion into the shape shown and then may be cut into the required short lengths 18, after which the shaded portions 19 may be removed by a straight milling process, resulting the wing lugs 20 a d aliecting the outside diameter of the cylindrical body portion 21. By this process the members may be manufactured in volume with greater accuracy, at less cost, and with greater uniformity than is the case where the members are formed by a machining process from a SOll rod or insulating material.

It has been found in practice that vacuum tubes employing indirectly heated cathodes and using alternating current as the source of heat energy must be accurately proportioned and designed in order to reduce the undesirable noises to a minimum. The embodiments hereinabove described permit extremely accurate manufacture and assembly, since the spacer members shown may be formed by an extrusion process. It has been found that when the members are made from material of the character dis *losed in application Serial No. 332,555, tiat they may be accurately formed by entrusion into the shapes shown in the Figs. 1 to 6 inclusive. Vhile the use of insulator tubes has heretofore been proposed, in order that accurate and uniform results may be obtained, it was necessary to machine the parts, and in view of the smallness of the bores for receiving the filament wires this machining operation prevented volume production and resulted in a high cost and lack of uniformity in the bores. By means of ap Jlicants invention the closure members 3, l, etc. may be made as small as desired, and the bore therethrough may be formed in the one operation of shaping the members, namely during the extruding process. Consequently the cost of production is materially reduced and more accurate insulators are provided. For example, if it is desired to produce a member of the character shown in Fig. 7 by machining, the smaller diameter would have to be turned-down from the body and the bore would have to be effected by a boring tool with consequent liability to produce lack of concentricity throughout the bore. Furthermore the turning down process results in a somewhat rounded corner 27 (Fig. 7) and will prevent proper seating of the member within the cathode tube, which during the operation of the tube may result in vibration of the filament, and also detrimental to uniform overall length of the assembled heater element.

Referring to Fig. 9 there is shown a plan view, partly in section, of a three-electrode tube embodying the principles of the invention. The numeral 24 represents the evacuated glass envelope within which are mounted in any well known manner on supports 25 and 26 the plate-electrode 27 and the gridelectrode 28 respectively. Suitably mounted concentrically within the grid 28 is the electron emitting cathode comprising the fila' ment 29, cathode tube 30, and the filament spacer and closure members 31 similar to the corresponding elements of Figs. 1 and 2. Because of the small size of the members and their heat confining function the time elapsing between the initial heating of lilament 31 and the effective emission oi the electrons from cathode is reduced to min imum. Furthermore this smallness in size of the insulator enables the tube to be evacuated more quickly and completely since the area required to be heated for driving out occluded gases is very small. Furthermore this reduction in size of the spacer members reduces the mass which has to be supported by the cathode and lessens the chance of breakage during shipping, handling, etc.

While in the foregoing specific forms and shapes of the cathode and heater elements are disclosed, it is understood that the invention includes within its scope other forms. For example the cathode tube instead of being circular in cross section may be square, oval, etc. in shape. Similarly instead of employing an emissive coating in a metal tube,

the tube itself may be made of emissive material and other changes in the form, construction and constitution of materials may be employed as will be clear to those familiar with the art.

What we seek to secure by United States Letters Patent is:

1. In an electron emitter the combination of a hollow tubular member having an electron emitting surface, a looped filament within said member, and a bushing fitted within one end of said member, said bushing having a slot for receiving and retaining the looped end of said filament.

2. In combination a tubular electron emitting cathode, an insulator and spacer element fitted in one end of said tubular member and having a cylindrical body portion provided with narrow lugs.

3. In combination a tubular electron emitting cathode, an insulator element suitable for electron discharge devices having a main body portion fitted in the end of said tubular member, lugs formed integrally with said body portion, and a bore extending through said body portion, said bore in cross section having one dimension much larger than the other dimension thereof, and a looped filament supported within said tubular member with the looped end of said filament resting in said bore.

4. In combination a tubular electron emitting cathode, an insulator bushing fitted Within one end of said cathode, said bushing having the portion outside of said tubular cathode of enlarged diameter, and a pair of grooves in the wall of said exterior portion, said bushing having a bore to receive the end of a heater filament.

5. A cathode structure comprising a thin wall metal tube having an electron-emitting coating thereon, an insulator in each end of the tube each having a pair of diametrically opposed lugs having limited circumferential extent and a bore therethrough and a heater wire supported within said tube out of con tact therewith and having its ends in said bores.

In testimony whereof We have hereunto set our hand on this 4th day of April, A. D.

HENRY L. GROVVLEY. ROBERT M. CROWLEY. 

